The hydrocracking technique has advantages including high adaptability to raw materials, high flexibility in production operation and product scheme, and high product quality, etc., and it can be used to directly convert heavy and poor-quality input materials into base materials for high-quality jet fuel, diesel oil, and lubricant, and produce chemical raw materials for ethylene from naphtha and tailings by steam cracking. It has become one of the most important deep processing techniques for heavy oils, and is widely applied increasingly in China and foreign countries. The core of a hydrocracking process is the hydrocracking catalyst. A hydrocracking catalyst is a typical bi-functional catalyst, with hydrogenation function and cracking function, wherein the hydrogenation function is usually provided by active metal elements in vulcanized state, such as W, Mo, and Ni, etc., while the cracking function is provided by a molecular sieve. Presently, modified Y molecular sieves are used the most widely in hydrocracking processes. However, owing to the properties of the acidic support in molecular sieves, molecular sieves are particularly sensitive to nitrides. Nitrides may be absorbed on the surface of a molecular sieve and thereby cause molecular sieve poisoning; consequently, the activity of the molecular sieve is severely degraded, and the molecular sieve can't work for long in the industrial production process. In addition, as the acid density in the molecular sieve increases, the nitrogen tolerance of the catalyst will be degraded severely. The method commonly used to solve that problem at present is to treat the Y molecular sieve by dealumination or dealumination and silicon reinsertion to reduce acid sites in the molecular sieve. However, with that method, dealumination happens inside and outside of the molecular sieve at the same time in the treatment process; consequently, the activity of the molecular sieve is severely decreased as the acid sites are reduced, while the silica-alumina mole ratio in the molecular sieve is increased. Hence, there is a contradiction between improving the nitrogen tolerance of the catalyst and keeping the hydrocracking activity of the catalyst, and it is difficult to make a trade-off between the two aspects through a conventional molecular sieve modification process.
In CN101450320A, a hydrocracking catalyst that contains a Y molecular sieve and a method for preparing the hydrocracking catalyst are disclosed. The catalyst comprises a hydrogenation active metal material and a support composed of a modified Y molecular sieve and alumina, wherein the modified Y molecular sieve has 750-850 m2/g specific surface area, 0.35-0.48 ml/g total pore volume, 90-130% relative crystallinity, 2.437-2.445 nm crystal cell parameter, silica-alumina mole ratio equal to 15-70, 0.5-1.0 mmol/g acid content measured by NIS, ratio of B-acid/L-acid greater than 7.0, and sodium oxide content ≤0.05 wt %. Specifically, the patent document discloses that the modified Y molecular sieve is prepared by dealumination and silicon reinsertion with ammonium hexafluorosilicate and hydrothermal treatment, and then treatment with a mixture solution of aluminum salt and inorganic acid or organic acid.
In CN101618348A, a hydrocracking catalyst support and a method for preparing the hydrocracking catalyst support are disclosed. The support contains modified Y molecular sieve, amorphous silica-alumina and alumina, wherein the modified Y molecular sieve has 750-850 m2/g specific surface area, 0.35-0.48 ml/g total pore volume, 90-130% relative crystallinity, 2.437-2.445 nm crystal cell parameter, silica-alumina mole ratio equal to 15-70, 0.5-1.0 mmol/g acid content measured by NIS, ratio of B-acid/L-acid greater than 7.0, and sodium oxide content ≤0.05 wt %. Specifically, the patent document discloses that the modified Y molecular sieve is prepared by dealumination and silicon reinsertion with ammonium hexafluorosilicate and hydrothermal treatment, and then treatment with a mixture solution of aluminum salt and inorganic acid or organic acid.
In CN1253988A, a nitrogen-tolerant hydrocracking catalyst for increasing the yield of middle distillates is disclosed, comprising: 10-60 wt % amorphous silica-alumina, 10-40 wt % VIB metal oxide, 1-10 wt % VIII metal oxide, and 1-10% IVB metal oxide, wherein the catalyst contains 1-40 wt % modified Y zeolite, which has silica-alumina mole ratio equal to 9-15, 95-100% crystallinity, 750-950 m2/g specific surface area, 24.23-24.45×10−10 m crystal cell parameter, with pores in pore diameter >1.7×10−10 m accounting for 40-70% of the total pore volume. The catalyst can be used for producing middle distillates from heavy distillates by one-stage hydrocracking, and the nitrogen content in the input material in the cracking section can be 100 μg/g, but the catalyst has poor activity.